Remember the old catchcry "its flooded" when an engine failed to start. Lawnmower. tractor, car, anything.
Miken's post prompted me to post this, well done Miken on your diagnosis!
One point which cannot be made strongly enough is that the engine if known to be flooded is started with the throttle closed. Somewhere in the system there will be a pool of petrol some of which can be sucked in to drown the plugs. If we give it full throttle, even though there will be no vacuum, the airflow will be at maximum which will stir up the puddle and suck straight petrol into the cylinders. Bad enough when cranking but as soon as one cylinder fires airflow increases hugely and petrol will certainly be sucked right in.
Unfortunately we are not out of the woods yet as the firing and stopping will be exactly the same whether it is flooded or the flooding is cleared and it is simply in need of some choke. Two choices, pull a couple of plugs or take a risk and pull the choke out. Try starting with just a little throttle?
Even if the engine starts and idles the petrol might still be there and opening the throttle will suck it in and put the fire out again.
Rick's Austin will have a manifold drain (many makes did) to avoid all of this. There is a hole from the inlet manifold through a hotbox bolt which is drilled and cross-drilled, then a thin copper tube fitted, down through a tab on a sump bolt. The A4 will not flood but there well be a petrol stain on the floor if anything goes wrong.
We have done nothing about raw petrol getting into the manifold, anyone with an updraught carb might think they are exempt from all this but tractors in particular are capable of sucking petrol from an updraught into the cylinders.
Accelerator pumps also complicate the situation as every time the throttle is pushed down the pool grows.